Apparatuses of the above indicated, general kind are known through for instance Swedish patents Nos. 500 894 and 500 428. These known apparatuses which are those which are presently mainly used for cleaning ventilation ducts and the like, and although they in many cases operate satisfactorily they suffer from a great number of relatively serious shortcomings. A very serious disadvantage of these known apparatuses is that their design results in a very high consumption of air and that they therefore require compressors having high capacity and a correspondingly high price. In the case of the first-mentioned one of the known apparatuses the high consumption of air depends mainly on the fact that the pressure medium while being the driving or propelling medium for the apparatus also all by itself performs the cleaning function, and as regards the last-mentioned one of the known apparatuses this is originally and intentionally, designed for a large pressure medium flow of up to 6.3 m.sup.3 /min.
Other shortcomings of the known apparatuses is that they have problems engaging the wall of the channel during operation, which in both cases must be solved by means of some kind of auxiliary friction means on the apparatus for increasing the friction against the channel wall; that they have a tendency to turn in the channel during operation due to the fact that the pressure medium exhaust openings are provided on a sidewall of the housing of the apparatus and are directed obliquely backwards towards the channel wall; and that they, due to their design as an "outer turbine", i.e. in both cases one portion of the housing of the apparatus is in practice designed as the turbine rotor, while another portion of the housing is designed as an inner turbine housing, experience bearing problems in the bearing between the inner turbine housing and the rotor, said problems being caused by to the heavy impacts against the channel wall which may occur due to unbalance and the relatively great moment developed which such a design as an "outer turbine".
A basic object of the present invention is therefore to provide an apparatus of the kind indicated in the introduction, which eliminates or at least substantially reduces the above discussed problems in connection with the prior art apparatuses, and which more specifically presents better performance and reliability combined with low air consumption and simple manufacturing.